TurboIMAGE/XL Database Management System Reference Manual MPE/iX V6.5 (30391-90011)

218 Chapter5
TurboIMAGE/XL Library Procedures
DBOPEN
Discussion
A process can concurrently use the database through independent, unique access paths by
issuing as many as 127 calls to DBOPEN (63 calls per database) and specifying a different
base array in each call. Subsequent calls to other TurboIMAGE/XL procedures must use
the appropriate base array so that the correct base ID is used.
CAUTION Although a single process can call DBOPEN a maximum of 127 times (63 per
database), DBOPEN can encounter an MPE/iX system limit and fail. For
example, DBOPEN would fail if the limit was exceeded for mapped file space or
if the process attempted to open more than the allowable number of files.
The database activity controlled on one access path relates to that controlled on other
access paths in the same way the database activity of one process relates to that of
another. The access modes established by each DBOPEN call must be compatible, but
otherwise the activity controlled by each access path and the pointers maintained by it are
completely independent. The only exception to this access path independence relates to
locking. If a process makes a lock request on one access path, it cannot issue a lock on
another access path unless the program has multiple RIN capability (CAP=MR) or first
calls DBUNLOCK to release the locks on the first access path.
DBOPEN performs expansion recovery if necessary. During the first open of the database
using any open mode, DBOPEN automatically performs expansion recovery for any detail
data set with the "expansion in progress" flag turned on and a previous DBPUT capacity
expansion had not completed. Recovery correctly adjusts the data set free count and the
root file data set capacity fields using the actual data set file size. Use the SHOW CAPACITY
command in DBUTIL to detect if recovery is required for the data set. If the message,
"dynamic capacity expansion in progress flag is on," is displayed for the data set, and
asterisks are in the "no. of entries" and "%max cap" fields, then recovery is required for the
data set(s). QUERY or any application performing the first DBOPEN of the database can be
used to recover the detail data set capacity. Use DBChange Plus or a third-party
application to change an existing detail data set to have parameters for dynamic
expansion.
If the database is enabled for logging, and the program calls DBOPEN in one of modes 1-4,
then TurboIMAGE/XL attempts to access a log file using the MPE/iX OPENLOG intrinsic.
OPENLOG succeeds only if the following have been completed:
1. A valid log identifier and log password have been set into the database root file using
the DBUTIL >>SET command, and
2. A corresponding system log process has been initiated by the console operator to handle
any calls to the logging system.
If OPENLOG fails, DBOPEN also fails and returns an appropriate error condition. If OPENLOG
succeeds, DBOPEN causes a log record to be written which includes such information as
time, date, user name, user program, mode, and security class. (Refer to appendix E for a
full description of log record contents and formats.)
A process is logging if it successfully opens a database in one of modes 1-4, and the
database is enabled for logging. A program does not log if it opens in one of modes 5-8, or if
the database is not enabled for logging.